Re: [PATCH 1/1] staging: hv: Fix race condition on IC channel initialization(modified)

[Jiri Slaby]

On 05/26/2010 11:25 PM, Haiyang Zhang wrote:
>> From: Greg KH [mailto:gregkh@xxxxxxx]
>>> +			    VmbusChannelOpen(newChannel, 2 * PAGE_SIZE,
>>> +					     2 * PAGE_SIZE, NULL, 0,
>>> +					     hv_cb_utils[cnt].callback,
>>> +					     newChannel) == 0) {
>>> +				hv_cb_utils[cnt].channel = newChannel;
>>> +				mb();
>>
>> What is the mb() call for?  Why is it necessary?  (hint, if you need it,
>> something else is really wrong...)
> 
> It ensures the channel assignment happens before the wakeup call: 
> osd_WaitEventSet(ic_channel_ready), if the compiler optimization re-arrange 
> the execution order. 

wake_up() is a barrier, you don't need the mb() there.

BTW osd_WaitEventSet et al. can be easily converted to completion.

-- 
js
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/